The rocks at Myrtleville Bay are sedimentary rocks, consisting mainly of layers of sandstone, siltstone and mudstone. They are Devonian in age and are generally referred to as ‘The Old Red Sandstone’. To see the red rocks you must start at the north eastern end of the Bay, near Fennel’s Bay. Here the rocks layers are the oldest, and are almost vertical.

Photograph 1		 As you walk towards the Bunnyconnellan restaurant, you are walking through time. The rock layers get younger, and green sandstones are inter-layered with the red. These green/brown layers become dominant as you approach Myrtleville beach.(see photograph 1). The colours of the rocks, together with other detail, indicate that they were laid down as sediment in a non-marine environment, in large rivers,
on river flood plains and in coastal areas.Just beneath Bunnyconnellan the nature of the rock changes. In some layers, small trace fossils can be seen. They record the burrowing of small worms into the original sediment, and indicate a shallow marine environment. This marks the beginning of a marine flooding of the land which lasted for several million years.
The ages of the rocks have been determined in the Geology Department in University College Cork, by collecting samples and investigating the fossil pollen and spores contained within some layers. Since these pollen and spores evolve with time, any particular form is characteristic of a certain age. The evidence indicates the rocks are Late Devonian in age, that is approximately 360 million years old.
This part of Ireland was situated 10 degrees south of the equator when these sediments were being laid down. Rocks retain the magnetic properties of the latitude at which they formed, so helping geologists to reconstruct the ancient geography.The cliffs adjacent to Myrtleville Bay are composed of unconsolidated Quaternary sediment.
The sediment lies directly on top of the Devonian bedrock. These cliffs are vulnerable to coastal erosion, and recent slumping is visible. The slumped material soon becomes vegetated. In the storms of October 2004, sections of vegetated slumped material were washed away by the sea, leaving Quaternary sand and clay newly exposed (see photograph2). These thin alternating layers show evidence of frequently changing conditions during the past 10, 000 years.
Photograph 2
Sea-level has also changed dramatically during this time. South of Bunnyconnelan, bright red sand in the cliff is the remains of an ancient beach. It is now well above the present high tide and is referred to as a ‘raised beach’. Raised beaches are found around the coastline of Ireland, marking a time when the sea-level was higher.
Geologists come from all over Ireland to study the succession of rocks at Myrtleville Bay. In addition there has been a number of International Field trips to the area.